At the start of the 1980s, a new type of wound dressing was launched by Smith&Nephew, a company which manufactures wound dressing products. The product, which is still on the market and is sold under the name OpSite™, is based on an invention that is described in British patent GB1280631. The dressing consists of a very thin polyurethane film, ca 25 micrometres, that is coated with a thin, self-adhesive layer of adhesive, also ca 25 micrometres. Due to its thinness, the film is very flexible and pliant. It can be attached securely and can seal relatively tightly around wounds on non-smooth skin surfaces, both convex and concave. Any wrinkles that are formed, however, sometimes produce thin channels, through which fluid is able to leak. This dressing, which was totally unlike all previous dressing products, formed an entirely new category known as self-adhesive film dressings. More companies followed with similar products, and today large numbers of film products with a similar function and characteristics are available on the market. These film dressings soon found an important application for the securing and protection of intravenous cannulas (for example of the Venflon cannula type). They are also used to cover different types of wound, for example sites from which skin is removed in conjunction with skin transplantation.
A significant factor for the major sales success of the film products was, apart from the above-mentioned characteristics, the successful development of effective application systems. The thin dressings are extremely difficult to handle without specially designed application systems. For this purpose, therefore, a more rigid carrier material is normally attached in a removable fashion to the non adhesive-coated side of the film in order to impart rigidity to the product, which would otherwise easily become tangled up in conjunction with its application to the skin. The carrier material, which imparts rigidity to the thin film, is not removed from the product until the self-adhesive film has been applied in the intended place.
The film dressings have been improved in a variety of ways in more recent times. Specially designed intravenous securing films have been developed with a perforated narrow slot to leave space for the tube connection of the intravenous cannula and, in so doing, to improve its function. A number of film dressings have been provided with a wound pad which covers the central part of the adhesive-coated side (a so-called island dressing), so that a certain degree of absorption of fluid from the wound is achieved when the film dressing is applied over a wound.
The above-mentioned category of dressing, self-adhesive film dressings, has nevertheless shown itself to have a number of weaknesses:
1. Relatively aggressive adhesives have been used in order to achieve a secure fixing without the risk of the film dressings becoming loose. The manufacturers selected aggressive types of adhesive in order to satisfy themselves that the dressings are already attached to the skin sufficiently securely immediately after application. The reason for this is to avoid the intravenous cannula becoming loose inadvertently, which would constitute a risk to the safety of the patient. It is also wished to avoid wound fluid from weeping wounds penetrating the adhesive joint between the film and the skin and leaking out onto the healthy skin outside the dressing. The types of adhesive used today possess the characteristic that the adhesion to the skin increases substantially with time. The adhesive strength of many film dressings is multiplied several times over after a few hours or days, compared with the adhesion immediately after application. When film dressings are attached too strongly, they often cause reddening and pain when they are removed from the skin. They also damage the barrier function of the skin because they take with them epithelial cells from the skin. In spite of this, a manufacturer may select these types of adhesive because the most important consideration is for the adhesion to be sufficiently good directly after application.
2. In the course of examining the protection against leakage from film dressings, the applicants identified an unexpected weakness in the ordinary film dressings. Studies under the microscope revealed that fluids are capable of spreading easily under the film dressings, in spite of the fact that they are apparently securely attached to the skin with an entirely tight seal. It was found that fluid was capable of spreading for a number of centimetres under the dressings via the naturally occurring microscopic folds in normal skin. Because the leakage consists of very small quantities and is not visible if the inward leakage of colourless fluids is examined, this has been disregarded previously. The phenomenon, known as micro-leakage, was first observed when the fluid was dyed with a strongly coloured pigment. The transport of fluids beneath the film dressings can constitute a major risk to patients because micro-organisms could be transported from outside or from the skin under the dressing and into the wound. An infection from a central venous catheter (CVC), which will often have been covered with a film dressing, can constitute a risk to the patient's life. Manufacturers of film dressings often market these as “shower proof”. When taking a shower, the risk of the aforementioned type of micro-leakage naturally increases considerably.
3. The adhesive on the film dressings that are sold today exhibits high adhesion to hairs. Because these dressings are often applied to hairy skin surfaces, pain and pulling out of hairs often occurs when the dressings are removed.
The object of the present invention is to solve the aforementioned problems while retaining all the advantages offered by the thin elastic carrier material, such as their softness and pliability, which is the unique strong feature of the film dressing product type.